I am guessing that it is because those users are important or have a answer to the question in ....question....
or that they are important to the Question and answer and therefore comes up in the search. It could just be that the person is related to the Q in other Qs. This doesn't make much sense does it.....?

For those they are probably shown because they are linked more across the site. Mew has many answers, maybe one of the most. Though for some reason it's showing an account called "Mew :3" ... did Mew create that after he changed his name back to regular "Mew"?